This disclosure generally relates to systems and methods for assessing the performance of a system (e.g., a system having a radiofrequency or optical aperture) installed onboard a sensing aircraft.
As mission requirements push sensing aircraft out to farther stand-off ranges, the need to characterize installed aperture performance is critical for establishing operational capabilities and limitations for onboard communication and sensor systems. Where ground-based testing may prove infeasible due to facility limitations, vehicle scale, or required geometry, airborne testing provides an alternative means of gathering the required data. Current methods of execution for airborne flight profiles involve flying pre-planned trajectories with ground controller-aided maneuvering to track the target depression angle. The ground controller uses an estimate of the test platform's position and attitude to relay maneuvering corrections required to track the target depression angle. The pilot of the airborne test platform responds to the verbal guidance with no explicit onboard feedback of the depression angle tracking error. The primary challenges for existing assessment methods are the limited precision and repeatability in tracking the target depression angle and the limited ability to accommodate disturbances and system constraints in real-time. Latency in ground controller commands to the pilot, lack of onboard tracking error displays, and the challenges in accounting for environmental effects (winds, off-nominal geometry, etc.) are significant factors affecting the data quality of existing solutions. There can be several seconds of time delay in the controller-pilot-aircraft control loop. The ground controller must interpret the estimated vehicle state and issue correction maneuvers based on intuition and experience. After radio relay of corrections, the pilot must interpret and execute the commands smoothly and precisely without the benefit of onboard tracking cues. Without onboard feedback, the pilot has no indication of the magnitude or rate of the depression angle tracking error. The ground controller is generally limited to discrete attitude correction commands and qualitative rate guidance which is insufficient for precise tracking of the target depression angle. The ability to repeat the same trajectory for comparison and validation purposes can also be a challenge. Environmental effects like winds aloft and off-nominal profile setups offer additional challenges, introducing uncertainties that are difficult to accommodate with existing assessment methods. Constraints exist for both the vehicle kinematics (speed, altitude, etc.) and the special test equipment (minimum/maximum range, look rate, cross-polarization angle, etc.). Assessment profiles are pre-planned to avoid constraints to the maximum extent possible. Responding to disturbances in real-time often results in sub-optimal trajectories that reach constraints sooner than planned, resulting in insufficient data.
There is a need to improve data quality and reduce costs when conducting airborne testing to assess installed aperture performance or for field measurement of mission systems.